Turkey's purchase of the S-400 systems, which are not compatible with NATO defences, has unnerved the United States and NATO member countries, which are already wary of Russia's presence in the Middle East.

Akar told Anadolu that selected personnel would be sent to Russia to receive training and return to work in Turkey, according to Hurriyet. It was not clear where he was speaking.

The United States has warned Turkey that going through with the purchase of S-400s could result in Washington imposing sanctions and halting other existing procurements, but Ankara has pressed on with the deal.

Turkey has said that its Western allies, namely the United States, have failed to cooperate with it in its efforts to boost its defence capabilities, and that Ankara has had to look outside of the NATO to meet its needs.

While pursuing S-400 project, President Tayyip Erdogan has said Turkey's ties with NATO remain strong, and Ankara has sought to secure defence deals with other countries as well.

Last year, Turkey signed a letter of intent with France and Italy to strengthen cooperation on joint defence projects. As a first step, the Franco-Italian EUROSAM consortium and Turkish companies will look into a system based on the SAMP-T missile systems.

Turkey is also buying Lockheed Martin F-35 Joint Strike Fighter jets from the United States, but United States has warned that their purchase could be jeopardised if it does not drop the S-400 purchase plan.

"There were some issues stemming from the S-400s, political and judicial developments, but the political and military conditions we have now do not cause concerns," Akar told Anadolu.

Akar said the F-35 programme was continuing as planned, with the third and fourth jets to be delivered in March next year.

Erdogan has previously said that Turkey would continue to pay its instalments to procure the jets, but that it would look elsewhere if Washington decided to halt the delivery.

Turkey and the United States have also held talks on the possible sale of a Raytheon Co Patriot missile defence systems as an alternative to the S-400 systems. (Reporting by Tuvan Gumrukcu; Editing by Daren Butler and Mark Heinrich)